Swiss Pat. No. 374,068, published Feb. 14, 1964 (see Farmdoc 11,020); P. Truitt, L. R. Brammer and L. T. Creagh, J. Med. Chem., 8, 731(1965); and Chem. Abstr., 77, 151795d (1972) for H.-J. W. Vollmann, K. Bredereck and H. Bredereck, Chem. Ber., 105, 2933 (1972) disclose 3-(1-piperazinyl)-1H-isoindol-1-one derivatives. The latter derivatives are distinguished readily from the compounds of the present invention by having different substituents, two of which are at position 3 of the 1H-isoindol-1-one nucleus. The present compounds have only one substituent at that position. Chem. Abstr., 74, 64158t (1971) for R. R. Schmidt and E. Schlipf, Chem. Ber., 103, 3783 (1970) discloses 1H-isoindol-1-one derivatives bearing a single substituent at position 3. The latter compounds, which were prepared in the course of a chemical investigation, differ from the compounds of the present invention in that they lack the pyrazino substituent on the 1H-isoindol-1-one nucleus.